Radio signaling system



R. 5. OHL

RADIO SIGNALING SYSTEM Nov. 12, 1929.

Filed Sept. 23, 1925 INVENTOR 1?. .5. 0M BY ATTORNEY Patented Nov. 12,1929 UNITED STATES PATENT OFFICE RUSSELL S. OHL, OF NEW YORK, N. Y.,ASSIGNOR TO AMERICAN TELEPHONE AND TELEGRAPH COMPANY, A CORPORATION OFNEW YORK I RADIO SIGNALING SYSTEM Application filed September 23, 1925.SerialNo. 58,164.

" This invention relates to short wave signaling systems.

It has been found desirable in short wave signaling systems to use abeam of waves 5 for the transmission and reception of signals.

In order to setup a beam of waves a parabolic reflector may be employedtherefor, the parabolic reflector consisting of a plurality of elementsarranged on a parabolic surface around a transmitting or receivingaerial as a focus, each element being tuned to the frequency of theaerial. The length of each element is preferably about half a wavelength, but the length may be made greater or less than this byincluding either a condenser or an inductance therein.

But when a parabolic reflector is used for the transmission of a beam ofwaves, it is customary to employ another parabolic reflector for thereception of a similar beam of waves. Such reflectors are large andexpensive, and it therefore seems necessary to provide a system wherebya single reflector may be employed for both the transmission andreception of a beam of waves.

Accordingly, it is an object of this invention to provide a pair ofparabolic reflectors, one at each station, each being suitable for boththe transmission and reception of a polarized beam of waves.

While the nature of this invention will be pointed out withparticularity in the appended claim, the invention ltself, both as toits objects and features, will be more clearly understood from thedetailed descrip- I tion hereinafter following when read in connectionwith the acompanying drawing rep resenting one embodiment of theinvention. The apparatus at the two statlons shown in the drawing aresimilar and therefore the same reference characters have been employedin connection witlreach station, except that at one of the stations thereference characters are primed.

Referring to the drawing, two stations A and B are shown. At station Athere is a parabolic reflector PR consisting of a pluralityof elements aall arranged on a parabolic surface around an aerial R, sometimes calleda resonator. .An oscillation generator 0 is shown in the drawing forgenerating a very high frequency, for example, 20,025 kilocycles, thefrequency being constant within very narrow limits. This may be apiezo-clectric oscillator, or a vacuum tube oscillator controlled as tofrequency by means of a piezoelectric device, or a low frequencyoscillator having connected thereto in tandem a plurality of harmonicgenerators, or frequency multiplers, so as to change the low frequencyoscillations to high frequency oscillations.

A harmonic generator, or a frequency multiplier, is connected to theoscillation generator O including a vacuum tube VT having an inputcircuit and an output circuit. The output circuit of this vacuum tubeincludes the anode and cathode of the vacuum tube VT, the inductance band condenser 0. A variable condenser d is employed for tuning theoutput circuit of the vacuum tube VT to any frequency, preferably aharmonic of the frequency in the input circuit thereof, for example,40,050 kilocycles. Another variable condenser e and an inductance f areconnected to the output circuit of the vacuum tube VT for impressing thefre quency of the output circuit on the aerial R.

The reference character T represents a device which is employed forsuperimposing signals on a high frequency current supplied to the aerialR. This device may be a microphone, an alternator, or any device capableof transmitting signals which may be superimposed on a high frequencycurrent. A source of potential B supplies the necessary space current tothe anode of the vacuum tube VT. Current from the source of potential Bflows through choke coils LC and HO and the inductance b, the choke coilHO being employed for preventing the transmisslon of frequencies of40,000 kilocycles or more, and the choke coil LC being employed forpreventing the transmission of a frequency of 5O kilocycles. However,current of a frequency of 50 kilocycles passes through the condenser gand is impressed on the primary winding of'the transformer h. Due to thecoupling existing between the primary and secondary windings of thetransformer h, this current is also impressed on the secondary windingthereof, and thereafter upon the input circuit of an amplifier AM. Thisamplifier AM may be any amplifier well known in the art, preferably avacuum tube amplifier.

The output circuit of this amplifier is connected to a detector D whichhas a receiving device connected in the output circuit thereof. Thisreceiving device receives the signals which are superimposed on thecurrent of the frequency of kilocycles which are detected by D.

The apparatus at station B is similar to the apparatus at station A, thereference characters for the apparatus at station B being the same thereference characters at station A except that they are primed. V

The arrangements of this invention operate in the following manner:

The oscillation generator 0 transmits a high frequency, for example,20,025 lrilocycles, to the input circuit of the vacuum tube VT. Theoutput circuit of this vacuum tube is tuned by the variable condenser (Zto a harmonic of the frequency in the input circuit, for example, 40,050kilocycles. For the transmission of signals from the station A to thestation B the transmitter T transmits signals through the choke. coilsLG and HC, and these signals are superimposed on the high frequencycurrent in the output circuit of the vacuum tube VT. This high frequency current, modulated in accordance with the signals, is thentransmitted through the condenser e and inductance f to the aerial Byvirtue of the relation of the elements of the parabolic reflector PR tothe aerial R, a beam of polarized Waves of the frequency of 40,050lrilocycles modulated in accordance with signals is transmitted fromstation A to the parabolic reflector at station E.

This beam of polarized waves strikes the inner surface of the parabolicreflector PR at station B. Thus, this beam of high frequency wavesmodulated in accordance with signals is transmitted by the aerial R atstation E to the output circuit of the vacuum tube VT through theinductance 7" and the condenser c. There are also impressed on theoutput circuit of the vacuum tube V T the oscillations of a harmonic ofthe frequency of the oscillation generator 0. The frequency of thisharmonic may be 40,000 kilocycles.

Thus the high frequency oscillations, for example, 40,050 kilocycles,received at tation B, modulated in accordance with signals, and theoscillations of the frequency of the harmonic of the oscillationgenerator O, for example, 40,000 kilocycles, beatin the output circuitof the vacuum tube VT to produce, among other frequencies, a differencefrequency, for example, 50 lrilocycles. This difference frequency, forexample, 50 kilocycles,

is impressed on the primary winding of the transformer the choke coil HGopposing the flow of current of the frequency of 40,000 lrilocycles, orof higher frequencies, and the choke coil LC opposing the flow ofcurrent of the frequency of 50 kilocycles in order to permit this latterfrequency to be transmitted to the primary winding of the transformer h.This difference frequency, or intermediate frequency, also hast-hesignals transmitted from station A impressed thereon and is amplified bythe amplifier AM. After amplification by the amplifier AM this frequencyis transmitted to the detector D so that the signals may be derivedtherefrom.

' Similarly, signals from the transmitter T superimposed on the locallygenerated high frequency, for example, 40,000 lrilocyeles, aretransmitted by the parabolic reflector PR at station E to the parabolicreflector PR at station A. This high frequency upon which signals aresuperimposed is beaten With the high frequency generated at the stationA in the output circuitof the Vacuum tube VT at station A, for example,40,050 kilocycles, so that an intermediate frequency, for example, 50kilocycles, results which is amplified by the amplifier AM and impressedon the detector D after being amplified by the amplifier AM so that thesignals may be derived therefrom.

It Will be understood that in the arrangements of this invention, asdisclosed, signals cannot be transmitted simultaneously from station Aand stationB by reason of the fact that there will be intermodulation ofthe signals and neither signal will be understood. But the invention isnot so limited,.for arrangements may be provided to permit thesimultaneous transmission and reception of signals between two or morestations Without intermodulation.

It will be understood that the frequencies referred to herein are merelyillustrative and that other frequencies may be employed in practice asconditions necessitate.

While the invention has been disclosed in one particular embodimentwhich is deemed desirable, it is to be understood. that it is capable ofembodiment in other and varied organizations Without departing from thespirit and scope ofthe inventionas defined in the appended claim.

What is claimed is:

A system for signaling between two stations, in which each stationincludes, in combination, a low frequency oscillator, a vac uum tubesystem having a grid circuit anda plate circuit, said vacuum tubesystembeing employed for locallyproducing a predetermined harmonic ofthe current of said oscil later of a frequency suitable for transmisofthe vacuum tube system and modulating the high frequency oscillationsderived therefrom, a parabolic reflector coupled to the plate circuit ofthe vacuum tube system, said parabolic reflector being employed fortransmitting as a polarized beam said high fre vthe vacuum tube systemso as to produce oscillations of an intermediate frequency Well abovethe range of audibility and which is modulated by the received voicefrequency signals means for amplifying the intermediate frequency andits modulated voice frequency signals, and means for detecting saidreceived voice frequency signals.

In testimony whereof, I have signed my name to this specification this21st day of September, 1925.

RUSSELL S. OHL.

